Heat/light-stabilized polyamide compositions

ABSTRACT

Heat and light-stabilized polyamide compositions containing a stabilization system that includes copper oxide and KBr, and have an excellent preservation of color and of the mechanical properties thereof after exposure to heat or to light; these compositions are especially useful for producing shaped articles in the automotive field.

CROSS-REFERENCE TO EARLIER APPLICATIONS

This application is a continuation of copending U. S. patent applicationSer. No. 12/745,934, filed Sep. 8, 2010, which is a U. S. National Stageof PCT/EP2008/066528, filed Dec. 1, 2008 and designating the UnitedStates (published in French on Jun. 11, 2009 as WO 2009/071507 A1; thetitle and abstract were published in English), which claims priorityunder 35 U.S.C. §119 of Application No. 07/08445, filed in France onDec. 4, 2007, each earlier application hereby expressly incorporated byreference in its entirety and each assigned to the assignee hereof.

The invention relates to a heat- and light-stabilized polyamidecomposition comprising a stabilization system that comprises copperoxide and KBr, having an excellent preservation of the mechanicalproperties after exposure to heat or to light. The invention alsorelates to a process for manufacturing these compositions and especiallyto the use of these compositions for producing articles in theautomotive field.

Polyamide is a synthetic polymer widely used for the manufacture ofvarious articles, such as molded and/or injection-molded parts.Polyamide may experience damage when it is subjected to externalconditions or elements such as UV radiation, heat and/or bad weather.Damage can also be induced by the heat used during its manufactureand/or its forming. This instability is reflected by damage, losses inmechanical properties, and changes in color. These problems may becomecritical for a certain number of applications, such as in particularparts in the automotive field which are, in particular, subjected tohigh heat.

In order to improve the stability of the polyamides with respect to heatand/or light, it is known to combine them with particular stabilizers.Numerous additives are sold for this purpose. The use of copper iodideis known, for example, especially in combination with potassium iodidewhich is used in most cases and which provides good stabilizationproperties. It is also known to use more complex additives such ashindered phenolic antioxidant compounds, stabilizers having at least onehindered amine unit of HALS type or phosphorus-containing stabilizers.

However, there is a need to obtain polyamide compositions that performeven better as regards the stabilization with respect to heat and light,and that are obtained at lower cost.

The applicant has developed a novel polyamide composition that makes itpossible to obtain excellent preservation of the mechanical propertiesafter a long exposure to heat and to light. These compositions also havethe advantage of maintaining their initial color, even after a longexposure to heat and to light.

The present invention relates to a composition comprising at least onepolyamide matrix, a copper oxide and KBr.

The copper oxide may especially be Cu₂O (cuprous oxide) or CuO (cupricoxide). The copper oxide may be in powder form. The compositionespecially comprises from 0.001% to 2% by weight of copper oxide,relative to the total weight of the polyamide, preferably from 0.005% to0.5% by weight, particularly from 0.009% to 0.12% by weight.

The composition may also comprise other heat and/or light stabilizerssuch as KI, hindered phenolic compounds, stabilizers having at least onehindered amine unit of HALS type, or organic or inorganicphosphorus-containing stabilizers, such as sodium or manganesehypophosphite.

Use will preferably be made of a combination of copper oxide and KBr orKI.

In particular, a polyamide composition comprising Cu₂O and KBr, inparticular from 0.009% to 1.2% by weight of Cu₂O and 0.1% to 1.2% byweight of KBr, relative to the weight of the polyamide in thecomposition, is preferred.

The polyamide of the invention is especially selected from the groupconsisting of the polyamides obtained by polycondensation of at leastone aliphatic dicarboxylic acid with an aliphatic or cyclic diamine suchas PA-6,6, PA-6,10, PA-6,12, PA-12,12, PA-4,6, MXD-6 or between at leastone aromatic dicarboxylic acid and an aliphatic or aromatic diamine suchas polyterephthalamides, polyisophthalamides, polyaramides, or theirblend and (co)polyamides. The polyamide of the invention may also beselected from the polyamides obtained by polycondensation of at leastone amino acid or lactam with itself, the amino acid possibly beinggenerated by hydrolytic opening of a lactam ring such as, for example,PA-6, PA-7, PA-11, PA-12, or their blend and (co)polyamides. As a typeof copolyamide, mention may especially be made of the polyamidePA-6/6,6.

Polyamides of PA-6 type and polyamides of PA-6,6 type are particularlypreferred. A polyamide of PA-6 type is understood to mean a polyamidecomprising at least 90% by weight of residues of caprolactam oraminocaproic monomers. A polyamide of PA-6,6 type is understood to meana polyamide comprising at least 90% by weight of residues of adipic acidand hexamethylenediamine monomers.

The polyamides may have an apparent melt viscosity between 30 and 1200Pa.s, measured according to the ISO 11443 standard at a shear rate of1000 s⁻¹ and a temperature of 250° C., especially for polyamides of PA-6type ; or an apparent melt viscosity between 30 and 700 Pa.s, measuredaccording to the ISO 11443 standard at a shear rate of 1000 s⁻¹ and atemperature of 280° C., especially for polyamides of PA-6,6 type.

In particular, it is possible to use polyamides of variable molecularweight by addition, before or during the polymerization of the polyamidemonomers, or else in melt extrusion, of monomers that modify the lengthof the chains, such as, in particular, difunctional and/ormonofunctional compounds having amine or carboxylic acid functionalgroups capable of reacting with the polyamide monomers or the polyamide.

The expression “carboxylic acid” is understood to mean carboxylic acidsand derivatives thereof, such as acid anhydrides, acid chlorides andesters, for example. The term “amine” is understood to mean amines andderivatives thereof capable of forming an amide bond.

It is possible to use, at the start of, during or at the end of thepolymerization all types of aliphatic or aromatic monocarboxylic ordicarboxylic acids, or all types of aliphatic or aromatic monoamine ordiamine amines.

Use may very particularly be made of a polyamide of type PA-6,6, that isto say a polyamide obtained at least from adipic acid andhexamethylenediamine or salts thereof such as hexamethylenediamineadipate, which may optionally comprise other polyamide monomers. Use mayespecially be made, as polyamide, of a polyamide of type PA-6,6 obtainedby addition, during polymerization, of an excess of hexamethylenediamineand of acetic acid or a polyamide of type PA-6,6 obtained by addition,during polymerization, of acetic acid.

Polyamides according to the invention may also be obtained by blending,especially melt blending. It is possible, for example, to blend onepolyamide with another polyamide, or one polyamide with a polyamideoligomer, or else one polyamide with monomers that modify the length ofthe chains, such as, in particular, diamines, dicarboxylic acids,monoamines and/or monocarboxylic acids. It is possible, in particular,to add isophthalic acid or benzoic acid, for example at contents ofaround 0.2 to 1% by weight, to the polyamide.

The composition of the invention may also comprise copolyamides derived,in particular, from the above polyamides, or blends of these polyamidesor (co)polyamides.

Use may likewise be made of branched polyamides of high fluidity,especially obtained by blending, during polymerization, in the presenceof the polyamide monomers, at least one polyfunctional compoundcomprising at least three identical reactive functional groups of aminefunctional group or carboxylic acid functional group type.

It is also possible to use, as a polyamide of high fluidity, a starpolyamide comprising star macromolecular chains and, where appropriate,linear macromolecular chains. The polymers comprising such starmacromolecular chains are, for example, described in documents WO97/24388 and WO 99/64496.

These star polyamides are especially obtained by blending, duringpolymerization, in the presence of polyamide monomers, an amino acid orlactam such as caprolactam, with at least one polyfunctional compoundcomprising at least three identical reactive functional groups of aminefunctional group or carboxylic acid functional group type. Theexpression “carboxylic acid” is understood to mean carboxylic acids andderivatives thereof, such as acid anhydrides, acid chlorides and esters,for example. The term “amine” is understood to mean amines andderivatives thereof capable of forming an amide bond.

Preferably, the polyfunctional compounds are selected from the groupconsisting of: 2,2,6,6-tetrakis(β-carboxyethyl)cyclohexanone, trimesicacid, 2,4,6-tri(aminocaproic acid)-1,3,5-triazine (TACT) and4-aminoethyl-1,8-octanediamine, bishexamethylenetriamine,diaminopropane-N,N,N′N′-tetraacetic acid,3,5,3′,5′-biphenyltetracarboxylic acid, acids derived fromphthalocyanine and from naphthalocyanine3,5,3′,5′-biphenyltetracarboxylic acid,1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridinetricarboxylicacid, 3,5,3′,5′-bipyridyltetracarboxylic acid,3,5,3′,5′-benzophenonetetracarboxylic acid, 1,3,6,8-acridinetetracarboxylic acid, trimesic acid, 1,2,4,5-benzene tetracarboxylicacid, diethylenetriamine, trialkylene tetramines andtetraalkylenepentamines, the alkylene preferably being ethylene,melamine, and polyalkylene amines, such as for example the Jeffamine T®compounds from Huntsman, especially Jeffamine T403®(polyoxypropylenetriamine).

The composition according to the invention may comprise between 20 and80% by weight, preferably between 20 and 60% by weight, and morepreferably between 35 and 55% by weight of polyamide, relative to thetotal weight of the composition.

The polymerization of the polyamide of the invention is especiallycarried out according to the conventional operating conditions forpolymerization of polyamides, in continuous mode or batch mode.

Such a polymerization process may comprise, briefly:

-   -   heating the blend of polyamide monomers, and optionally of        polyfunctional, difunctional and/or monofunctional compounds,        with stirring and under pressure;    -   holding the blend under pressure and temperature for a given        time, with removal of water vapor via a suitable device, then        depressurization and holding for a given time at a temperature        above the melting point of the blend, especially under        autogenous pressure of water vapor, under nitrogen or under        vacuum, in order thus to continue the polymerization by removal        of the water formed.

At the end of polymerization, the polymer can be cooled, advantageouslywith water, and extruded in the form of rods. These rods are cut up inorder to produce granules.

The composition according to the invention may comprise between 20 and80% by weight, preferably between 20 and 60% by weight, and morepreferably between 35 and 55% by weight of polyamide, relative to thetotal weight of the composition.

The copper oxide may be added in various ways in order to produce thecomposition according to the invention. It may especially be added atthe start of, during or at the end of the polymerization of thepolyamide, especially for polyamides of type PA-6,6. It may also beadded as a blend with the polyamide.

The composition may also comprise fillers conventionally used forproducing polyamide compositions. Mention may especially be made ofreinforcing fibrous fillers, such as glass fibers or carbon fibers, ororganic fibers, non-fibrous fillers, such as particulate fillers,lamellar fillers and/or exfoliable or non-exfoliable nanofillers such asalumina, carbon black, clays, zirconium phosphate, kaolin, calciumcarbonate, copper, diatomaceous earths, graphite, mica, silica, titaniumdioxide, zeolites, talc, wollastonite, polymeric fillers such as, forexample, dimethacrylate particles, beads of glass or glass powder.

In particular, the use of reinforcing fibers, such as glass fibers, ispreferred. Preferably, the most widely used fiber is glass fiber, of thechopped type, having a diameter between 7 and 14 μm, and a length ofless than 5 mm. These fillers may have a surface size that ensures themechanical adhesion between the fibers and the polyamide matrix.

The composition according to the invention may or may not compriseimpact modifiers, especially those having an elastomeric base comprisingfunctional groups that are reactive with the polyamide.

The composition may comprise, besides the modified polyamide of theinvention, one or more other polymers, preferably polyamides orcopolyamides.

The composition according to the invention may also comprise additivescustomarily used for the manufacture of polyamide compositions. Thus,mention may be made of lubricants, flame retardants, plasticizers,nucleating agents, catalysts, light and/or heat stabilizers,antioxidants, antistatic agents, dyes, matifying agents, molding aids orother conventional additives.

These fillers and additives may be added to the modified polyamide viastandard means suitable for each filler or additive, such as for exampleduring the polymerization or by melt blending.

The polyamide compositions are generally obtained by cold blending ormelt blending of the various compounds that are incorporated into thecomposition, especially the polyamide, the copper oxide and the KBr. Itis carried out at a higher or lower temperature and at a higher or lowershear stress depending on the nature of the various compounds. Thecompounds may be introduced simultaneously or successively. Generally,an extrusion device is used in which the material is heated, then meltedand subjected to a shear stress, and transported. Such devices are fullyknown to a person skilled in the art.

According to a first embodiment, all the compounds are melt blendedduring a single operation, for example during an extrusion operation. Itis possible, for example, to carry out a blending of granules of thepolymer materials, introduce them into the extrusion device in order tomelt them and subject them to a greater or lesser shear.

It is possible, according to particular embodiments, to produce moltenor non-molten premixes of some of the compounds before preparation ofthe final composition.

The composition according to the invention, when it is prepared using anextrusion device, is preferably packaged in the form of granules. Thegranules are intended to be formed using processes that involve meltingin order to obtain articles. The articles are thus constituted of thecomposition. According to one customary embodiment, the modifiedpolyamide is extruded in the form of rods, for example in a twin-screwextrusion device, which rods are then cut up into granules. The moldedparts are then produced by melting the granules produced above andfeeding the composition in the melt state into forming devices,especially injection-molding devices.

The composition according to the invention may be used for anyplastic-forming process, such as for example the process of molding,especially injection molding, extrusion, extrusion-blow molding or elserotomolding.

The present invention also relates to articles obtained by forming thecomposition according to the invention, for example by extrusion,molding or injection molding. Mention may be made, as articles, of thoseused in the automotive field, such as tanks, parts of air circuitsystems such as air distributors, air ducts, turbo outlet ducts, andparts of cooling circuit systems such as air coolers, radiator tanks andhousings.

Another subject of the present invention is a mixture comprising atleast one copper oxide and KBr. This mixture may, for example, compriseonly these two compounds, especially in powder form. This mixture mayalso comprise polyamide and at least copper oxide and KBr, especially inorder to form a masterbatch.

Specific terms are used in the description so as to facilitate theunderstanding of the principle of the invention. It should neverthelessbe understood that no limitation of the scope of the invention isenvisaged by the use of these specific terms. The term “and/or” includesthe meanings and, or, and also all the other possible combinations ofthe elements connected to this term.

Other details or advantages of the invention will appear more clearly inlight of the examples below, given solely by way of indication.

EXPERIMENTAL SECTION

The compounds used are the following:

Polyamide 6,6: PA-6,6 of average viscosity 140 in formic acid fromRhodia;

Cu₂O: from Fluka;

KBr: from Fluka;

Cul: from Fluka;

KI: from Fluka;

glass fibers: 99B from Vetrotex;

elastomer: Exxelor VA 1803 from Exxon; and

other additives: lubricant, pigment, etc.

The compositions are manufactured by melt blending using aWerner&Pfleiderer ZSK 40 co-rotating twin-screw extruder under thefollowing conditions: screw speed: 250 rpm, throughput: 40 kg/h,temperature profile: from 250 to 280° C., degassing: 0.9 bar. Thepolyamide, 50% by weight of glass fibers, 5% of elastomers, 0.2% ofadditives and a certain proportion of stabilizers as mentioned in thetable below are mixed. The stabilizers are added at the beginning of theextruder.

The granules obtained are then molded with a Demag Ergotech Viva 50-270press under the following conditions: temperature profile: 280-300° C.,mold temperature: 90-100° C., screw speed: 120 rpm, injection speed: 80cm³/s, backpressure: 10 bar.

The results of the properties of maintaining the mechanical propertiesbefore and after an aging test are mentioned in the following table:

TABLE 1 IMPACT STRENGTH IMPACT STRENGTH COMPOSITIONS BEFORE AGING AFTERAGING C1/without stabilizer 65 10 C2/0.08% Cul + 0.45% 65 22 KI 3/0.06%Cu₂O 67 18 4/0.06% Cu₂O + 0.45% 69 27 KBr

The percentages are expressed by weight relative to the weight of thepolyamide of the composition.

The impact strength (Charpy unnotched impact strength) is measuredaccording to the ISO 179-1/1 Fu standard. The aging is carried out inambient air at 200° C. for 31 days and then 7 days at 220° C.

What is claimed is:
 1. An admixture comprising at least one polyamideand a heat- and light-stabilizing amount of at least one copper oxideand KBr.
 2. The admixture as defined in claim 1, wherein said at leastone polyamide comprises at least one PA-6 polyamide or PA-6,6 polyamide.3. The admixture as defined in claim 1, wherein said at least onepolyamide comprises a blend of polyamides.
 4. The admixture as definedin claim 1, wherein said polyamide comprises at least one (co)polyamideand/or star polyamide.
 5. The admixture as defined in claim 1, whereinsaid at least one polyamide is a branched polyamide or a star polyamide.6. The admixture as defined in claim 1, wherein said admixture comprisesbetween 20 and 80% by weight of said at least one polyamide, relative tothe total weight of the composition.
 7. The admixture as defined inclaim 1, wherein said admixture comprises from 0.001% to 2% by weight ofcopper oxide, relative to the total weight of said polyamide.
 8. Theadmixture as defined in claim 1, wherein said admixture comprises from0.009% to 1.2% by weight of Cu₂O and 0.1% to 1.2% by weight of KBr,relative to the weight of said polyamide.
 9. The admixture as defined inclaim 1, further comprising at least one other heat and/or lightstabilizer selected from the group consisting of KI, hindered phenols,stabilizers having at least one hindered amine structural unit, organicphosphorus-containing stabilizers, inorganic phosphorus-containingstabilizers, sodium hypophosphite and manganese hypophosphite.
 10. Theadmixture as defined in claim 1, further comprising fibrous and/ornon-fibrous reinforcing fillers.
 11. The admixture as defined in claim1, wherein said fibrous fillers comprise glass fibers.
 12. The admixtureas defined in claim 1, further comprising impact modifiers.
 13. Theadmixture as defined in claim 1, wherein the at least one polyamidecomprises linkages of isophthalic acid or benzoic acid and saidisophthalic acid or benzoic acid is present in an amount from 0.2% wt %to 1 wt % of the composition.
 14. The admixture as defined in claim 1,wherein said at least one polyamide is: (a) a PA-6 polyamide having anapparent viscosity in a molten state ranging from 30 to 1200 Pa.s or 30to 700 Pa.s., measured according to ISO 11443, or (b) a PA-6,6 polyamidehaving an apparent melt viscosity ranging from 30 to 700 Pa.s, measuredaccording to the ISO 11443 standard at a shear rate of 1000 s⁻¹ and atemperature of 280° C.
 15. The admixture as defined in claim 1, whereinsaid at least one polyamide is a branched polyamide or a star polyamidehaving an apparent viscosity in a molten state ranging from 30 to 1200Pa.s or 30 to 700 Pa.s., measured according to ISO
 11443. 16. Theadmixture as defined in claim 1, wherein said at least one polyamide isa branched polyamide or a star polyamide having an apparent viscosity ina molten state ranging from 30 to 1200 Pa.s or 30 to 700 Pa.s., measuredaccording to ISO 11443, and said at least one oxide of copper comprisesCu₂O.
 17. The admixture as defined in claim 1, wherein the at least onepolyamide comprises linkages of isophthalic acid or benzoic acid, saidat least one polyamide having an apparent viscosity in a molten stateranging from 30 to 1200 Pa.s or 30 to 700 Pa.s., measured according toISO 11443, and said isophthalic acid or benzoic acid is present in anamount from 0.2% wt % to 1 wt % of the composition.
 18. The admixture asdefined in claim 17, wherein said at least one oxide of copper comprisesCu₂O.